Genetic diagnosis of trisomy 21 in chimpanzees (Pan troglodytes)

The most frequent chromosomal aneuploidy in humans, trisomy 21 (T21), has only been reported twice in the common chimpanzee (Pan troglodytes). In both cases, phenotypical traits were comparable to human T21 traits and were formally diagnosed through conventional techniques like chromosomal staining. Here, we present the first application of sequencing data as a diagnostic tool to compare chromosomal dosage imbalances in chimpanzees. By calculating the ratio of mapped reads on each chromosome between a case and a control, we observe a trisomic dosage imbalance on chromosome 21 in the case individual. While case numbers remain too low to be conclusive, evidence suggests that prevalence of T21 in chimpanzees could be lower than in humans. In future genetic testing of captive ape populations, the genetic diagnostic methods presented here will allow for a reliable and time-efficient assessment of the global prevalence of chromosomal dose imbalances in chimpanzees and other great apes.